Wearing ring and pump having the same

ABSTRACT

In a pair of wearing rings, the inner-cylinder wearing ring ( 5   a   , 5   b ) or the outer-cylinder wearing ring (4 a   , 4   b ) is formed of a carbon fiber reinforced plastic and constituted so that the coefficient of thermal expansion in the radial direction is −1×10 −6 /° C. to 30×10 −6 /° C. This makes it possible to maintain a clearance between the case wearing ring and the impeller wearing ring within a small fixed range even when the temperature rises due to rotation and when a high-temperature fluid is used. A pump provided with the wearing ring is excellent in stability and has a good efficiency.

TECHNICAL FIELD

[0001] The present invention relates to a wearing ring used in a pump, water wheel and the like.

BACKGROUND ART

[0002] In a general impeller-type pump that handles fluids, as shown in FIG. 1, an impeller 1 housed in cases (2 a, 2 b) is rotated by a main shaft 3 connected to a motor (not shown), whereby flows of fluid are taken from direction A, pressurized and discharged in the circumferential direction of the impeller, and the flows of fluid then join together within the cases and are discharged from an outlet (not shown). As wearing rings which are used as a bearing mechanism for the rotation of the impeller in the cases, case wearing rings (4 a, 4 b) and impeller wearing rings (5 a, 5 b) which are opposed thereto are paired and clearances provided between the pairs are lubricated by the fluid handled to thereby ensure smooth rotation. Thus, clearances are necessary. However, if the clearances are too large, the volume of fluid that leaks from the high-pressure side (outlet side) to the low-pressure side (suction side) increases, resulting in reduced pump efficiency.

[0003] Conventional wearing rings are formed of metals, ceramics, plastics, carbon, etc. Metal wearing rings are generally used because metals are the most inexpensive materials of all. However, in the case of small clearances, in particular, when a high-temperature fluid is handled, the impeller wearing rings can expand to a larger extent due to a temperature gradient and a temperature rise by rotation, with the result that the impeller wearing rings may sometimes come into contact with the case wearing rings resulting in seizure. For this reason, when metal wearing rings were used, it was necessary to design clearances of a large size. For example, in the case of a cylindrical wearing ring having a diameter of 80 mm, it is necessary that a clearance be about 0.4 mm (on diameter basis) and, therefore, this provided limitations to an increase in pump efficiency.

[0004] It is reported that in order to prevent the seizure of metal parts, one of a wearing ring pair is made of metal and the other is made of a ceramic or plastic material. However, ceramics have a drawback in that they are brittle and do not endure a long period of use. Plastic-made wearing rings have a drawback in that when they expand and come to the state of contact-sliding due to thermal expansion and swelling, their slidability is poor and, furthermore, a local temperature rise due to contact-sliding develops biting due to fusion bonding in the interface.

[0005] Also, in the Japanese Patent Laid-Open No. S63-129175 is described the fact that slidability is improved by using a composite material composed of a plastic material and a carbon fiber in the contact-sliding surfaces of a piston-type pump. However, in the case of an impeller-type pump etc., lubrication is performed by a fluid and, therefore, contact-sliding does not occur under usual conditions. When carbon and other composite materials are used, the slidability between these materials and metals may be improved. However, when contact-sliding occurs in an impeller-type pump, the pump efficiency decreases due to the increased loads and, therefore, it is not happened to positively effect the contact-sliding.

[0006] Also, in the Japanese Patent Laid-Open No. 2001-173660 is described the fact that it is possible to obtain a sliding bearing which has a high cooling effect, is very effective in removing foreign matter from water containing the foreign matter, and can operate under dry conditions (i.e., in the air) by using a sliding member provided, on a sliding surface thereof, with grooves formed through in the axial direction, the sliding member being fabricated of a carbon-fiber reinforced plastic which is molded by heating and hot working long carbon fibers wound in coil form with respect to the shaft center. However, although the sliding characteristics and the foreign matter removing effect are high, all carbon fibers are wound in the circumferential direction with respect to the shaft center, with the result that the following problems arise; that is, (A) the sliding bearing is vulnerable to damage by shock of impact of foreign matter, and (B) because the coefficient of thermal expansion in the radial direction is small, clearances are deformed by the heat generated by sliding during operation, making it difficult to obtain a stable pump efficiency. Furthermore, although according to this disclosure, various types of thermoplastic resins can be used as plastics to be used, (C) when thermoplastic resins are used, fusion bonding may sometimes occur under sliding conditions under which local contact such as eccentricity occur. Also, in the Japanese Patent Laid-Open No. H9-2643275 and Japanese Patent Laid-Open No. 2001-231213 is described a bearing each fabricated of a carbon fiber reinforced plastic which is formed from long carbon fibers wound in coil shape with respect to the shaft center by heating and hot working and problems similar to those described above arise.

DISCLOSURE OF THE INVENTION

[0007] The object of the present invention is to provide a wearing ring which enables a clearance between a case wearing ring and an impeller wearing ring to be maintained within a small fixed range even when the temperature rises due to rotation and when a high-temperature fluid is used, and a pump which is provided with the wearing ring, is excellent in stability and has a good efficiency.

[0008] The present invention discloses the following items.

[0009] 1. An inner-cylinder wearing ring or an outer-cylinder wearing ring each of which is used in a pair of wearing rings of the combination of inner-cylinder side and outer-cylinder side; wherein, the inner-cylinder wearing ring or the outer-cylinder wearing ring is formed of a carbon fiber reinforced plastic and has a coefficient of thermal expansion in the radial direction of −1×10⁻⁶/° C. to 30×10⁻⁶/° C.

[0010] 2. An inner-cylinder wearing ring or an outer-cylinder wearing ring according to item 1, in which its coefficient of thermal expansion in the radial direction is 3×10⁻⁶/° C. to 20×10⁻⁶/° C.

[0011] 3. An inner-cylinder wearing ring or an outer-cylinder wearing ring according to item 1, in which the above-described carbon fiber reinforced plastic contains carbon fibers oriented in the axial direction and carbon fibers oriented in the circumferential direction of the wearing ring and in which the ratio of (weight of axial carbon fibers): (weight of circumferential carbon fibers) is (1:10) to (100:10).

[0012] 4. An inner-cylinder wearing ring or an outer-cylinder wearing ring according to item 3, in which the ratio of (weight of axial carbon fibers): (weight of circumferential carbon fibers) is (15:85) to (85:1).

[0013] 5. An inner-cylinder wearing ring or an outer-cylinder wearing ring according to item 1, in which the carbon fibers in the carbon fiber reinforced plastic which constitutes an outermost layer of the inner-cylinder wearing ring or the outer-cylinder wearing ring are a fabric.

[0014] 6. An inner-cylinder wearing ring or an outer-cylinder wearing ring according to item 1, in which a matrix resin contained in the carbon fiber reinforced plastic is a thermosetting resin.

[0015] 7. An inner-cylinder wearing ring or an outer-cylinder wearing ring according to item 1, which is used in a pair of wearing rings in which a metal wearing ring is used as an opposed wearing ring.

[0016] 8. An inner-cylinder wearing ring or an outer-cylinder wearing ring according to item 1, in which the carbon fiber reinforced plastic is fabricated of continuous carbon filaments whose tensile modulus is in the range of 49 Gpa to 950 GPa.

[0017] 9. An inner-cylinder wearing ring or an outer-cylinder wearing ring according to item 1, which is used in a pump provided with an impeller having an impeller wearing ring and a pump casing having a case wearing ring.

[0018] 10. An inner-cylinder wearing ring according to item 1.

[0019] 11. An inner-cylinder wearing ring according to item 1, which is used in a pair of wearing rings in which a metal wearing ring is used as an opposed wearing ring.

[0020] 12. A pump having the inner-cylinder wearing ring or the outer-cylinder wearing ring according to item 9.

[0021] 13. A pump having the inner-cylinder wearing ring according to item 9.

BRIEF DESCRIPTION OF THE DRAWINGS

[0022]FIG. 1 is a sectional view of an example of the structure of an impeller-type pump;

[0023] FIGS. 2(a) and 2(b) are drawings for explaining the coefficient of thermal expansion in the radial direction;

[0024]FIG. 3 is a drawing of the relationship between the discharge rate and pump efficiency of pumps in embodiments and in a comparative example;

[0025]FIG. 4 is a drawing of the relationship between the discharge rate and total pressure of pumps in embodiments and in a comparative example; and

[0026]FIG. 5 is a drawing of the relationship between the discharge rate and shaft power of pumps in embodiments and in a comparative example.

DESCRIPTION OF SYMBOLS

[0027]1 Impeller

[0028]2 a, 2 b Case

[0029]3 Main shaft

[0030]4 a Suction side case wearing ring

[0031]4 b Back side case wearing ring

[0032]5 a Suction side impeller wearing ring

[0033]5 bBack side impeller wearing ring

[0034]7 Main body of impeller

[0035]8 Main body of case

BEST MODE FOR CARRYING OUT THE INVENTION

[0036] As described above, the invention relates to an inner-cylinder wearing ring or an outer-cylinder wearing ring each of which is used in a pair of wearing rings of the combination of inner-cylinder side and outer-cylinder side; wherein, the inner-cylinder wearing ring or the outer-cylinder wearing ring is formed of a carbon fiber reinforced plastic and has a coefficient of thermal expansion in the radial direction of −1×10⁻⁶/° C. to 30×10⁻⁶/° C. Preferably, which the coefficient of thermal expansion in the radial direction is 3×10⁻⁶/° C. to 20×10⁻⁶/° C.

[0037] The coefficient of thermal expansion in the radial direction is a numerical value determined with respect to a value of change of the diameter of a wearing ring caused by thermal expansion or contraction. That is, in the case of an inner-cylinder wearing ring, as shown in FIG. 2(a), when the outside diameter φ of the wearing ring changes to (φ+Δφ), this value is determined by Δφ/(φ·Δt). In the case of an outer-cylinder wearing rate, as shown in FIG. 2(b), this value is similarly determined from a change in the inside diameter φ of the wearing ring.

[0038] The inner-cylinder wearing ring or outer-cylinder wearing ring of the invention is preferably used in a pump provided with an impeller and a pump casing. And in this case, the inner-cylinder wearing ring of the invention is used as an impeller wearing ring, and the outer-cylinder wearing ring is used as a case wearing ring.

[0039] In the invention, when a wearing ring expands thermally, carbon fibers suppress the expansion and, therefore, the thermal expansion of the wearing ring can be efficiently reduced.

[0040] Although the inner-cylinder wearing ring or outer-cylinder wearing ring of the invention is most preferably used both on the inner-cylinder and outer-cylinder of a pair of wearing rings, the wearing ring of the present invention shows sufficient effect even when used on one side only. In particular, a wearing ring of the invention which is formed of a carbon fiber reinforced plastic is preferably used on the side where thermal expansion poses a problem. For example, when heat is apt to be applied to the inner-cylinder wearing ring or when the inner-cylinder wearing ring is apt to expand because an inner-cylinder substrate material has a larger coefficient of thermal expansion, it is preferred that the present invention be applied to the inner-cylinder wearing ring. And on that occasion, an inexpensive, general metal wearing ring can be used as an opposed wearing ring which is a counterpart of the pair.

[0041] Although a wearing ring of the invention can be used on the external peripheral surface of the piston of a suspension cylinder, it can be most preferably used in an impeller-type pump which handles fresh water, seawater, oil, etc. as a fluid.

[0042]FIG. 1 shows an example of pump of this structure. By paying attention to the wearing ring portions, we will observe that the suction-side impeller wearing ring 5 a and the suction-side case wearing ring 4 a are arranged in a pair and that the back-side impeller wearing ring 5 b and the back-side case wearing ring 4 b are arranged in a pair. All of the wearing rings in this example are formed in the form of cylinders having a prescribed thickness and length, and attached to the main body of impeller 7 and the main body of case 8, for example, as shown in FIG. 2.

[0043] In the pump of the invention, in the pairs of wearing rings, i.e., in the pair of 4 a and 5 a or the pair of 4 b and 5 b, it is necessary only that a wearing ring on one side be formed of a carbon fiber reinforced plastic. However, when on the suction side, for example, the wearing ring of the invention is applied to the impeller wearing ring 5 a and the case wearing ring 4 a is made of metal, it is generally preferable that also on the backside, in consideration of similar thermal conditions, the wearing ring of the invention be applied to the impeller wearing ring 5 b and that the case wearing ring 4 b be made of metal

[0044] The shape of the pump is not limited to that shown in FIG. 1 and can be changed according to pump capacity, kind of fluid, etc. For example, the diameter, thickness, axial length, etc. of wearing ring can be appropriately changed. The shape of the inner-cylinder or outer-cylinder wearing ring is generally cylindrical and the cylindrical type is easy to form and is hence preferable. However, other shapes known as the shape of wearing ring, for example, a circular conical shape may be adopted. Incidentally, the terms “outer cylinder” and “inner cylinder” used in this specification are intended for a discrimination between a wearing ring on the outer side and a wearing ring on the inner side, which form a pair, and is not intended to indicate solely “cylindrical shaped” wearing rings.

[0045] In a pair of wearing rings in which the inner-cylinder or outer-cylinder wearing ring using the carbon fiber reinforced plastic of the invention is used at least one side, it is possible to efficiently suppress thermal expansion and, therefore, so long as the center accuracy of the rotation axis is sufficiently ensured, contact of one wearing rings with the other wearing ring will not occur and seizure can be prevented even when clearances are set to equal to or smaller than 0.5% of diameter and even to equal to or smaller than 0.2% of diameter. In general, in consideration of the problem of center accuracy of the rotation axis, the clearance is not less than 0.02% and preferably not less than 0.05%.

[0046] For example, in the case of a wearing ring having a diameter of 80 mm, it is most preferable to set the clearance (difference in the diameter between the outer-cylinder inside diameter and the inner-cylinder outside diameter) to about 0.08 mm to about 0.15 mm.

[0047] Concretely, such wearing rings are formed as follows.

[0048] First, the carbon fiber reinforced plastic used in the invention is obtained by impregnating carbon fibers with a matrix resin to obtain a composite material.

[0049] Carbon fires used are those having a tensile modulus of 49 to 950 GPa and in particular, those having a tensile modulus of 230 to 620 GPa are preferable. In terms of the tensile strength, carbon fibers having a value of 1150 to 4510 MPa are preferable and in particular, those of 2450 to 4410 MPa are preferable. In terms of the coefficient of thermal expansion of carbon fibers (coefficient of linear expansion in the fiber direction), carbon fibers having a value of −1.5×10⁻⁶/° C. to 4×10⁻⁶/° C. are preferable. By using carbon fibers of such physical properties, the expansion of the matrix resin is suppressed and the coefficient of thermal expansion of the carbon fiber reinforced plastic itself is reduced and, at the same time, the expansion and contraction of the substrate (main body of impeller, main body of case) to which the wearing rings are attached can be suppressed, with the result that the coefficient of thermal expansion in the radial direction as the wearing rings can be set to a desired value.

[0050] Pitch-base carbon fibers, PAN-base carbon fibers, etc. can be used as the carbon fibers of the invention. As required, these may be used in combination for making the carbon fiber reinforced plastic. It is preferable to select carbon fibers so that a desired coefficient of thermal expansion be obtained as wearing rings in consideration of the places of use, the material for the opposed counterpart of a pair of wearing rings.

[0051] As the carbon fibers, it is preferable to use continuous carbon filaments rather than short fibers. By winding continuous carbon filaments at least one turn in the circumferential direction of the wearing ring (in the case of a cylindrical shape, in the circumferential direction of the cylinder), the properties of carbon fibers can be efficiently utilized and furthermore the coefficient of thermal expansion in the radial direction as the wearing ring can be set to a desired value. It is preferable that in this manner, at least a portion of the carbon fibers in the carbon fiber reinforced plastic which constitute the wearing ring be substantially oriented in the circumferential direction. Furthermore, it is preferable that in order to prevent cracks etc. due to strains, carbon fibers oriented in the axial direction of the wearing ring (direction of rotation axis) be also present.

[0052] Usually, it is necessary only that carbon fibers be oriented in two directions, i.e., the circumferential and axial directions. The composition ratio (weight ratio) of carbon fibers in the circumferential direction to the carbon fibers in the axial direction is 1:(0 to 10). The composition ratio (weight ratio) of (carbon fibers in the axial direction): (carbon fibers in the circumferential direction) is preferably (1:10) to (100:10), especially preferably (15:85) to (85:15), and most preferably (15:85) to (20:10).

[0053] Incidentally, the circumferential orientation and axial orientation of carbon fibers may not always be precisely oriented to the circumferential and axial directions of the wearing ring. When 0° is defined as the axial direction of the wearing ring, the orientation of carbon fibers in the circumferential directions may be ±60° to 90° and preferably ±85° to 90°, and the orientation of carbon fibers in the axial directions may be 0° to 45° and preferably 0° to ±15°.

[0054] The volume content of carbon fibers in the carbon fiber reinforced plastic is preferably about 45 to about 70% by volume and especially preferably 55 to 65% by volume.

[0055] As a matrix resin that constitutes the carbon fiber reinforced plastic along with carbon fibers, a heat-resistant resin is preferable. Above all, polyether ether ketone resins, aromatic polyester resins, polyphenylene oxide resins, polysulfone resins, polyphenylene sulfide resins, polyamide imide resins, polyamide bismaleimide resins, etc. can be exemplified as thermoplastic resins; and phenol resins, epoxy resins, cyanate resins, urea resins, diallyl phthalate resins, polyimide resins, silicone resins, unsaturated polyester resins, etc. can be exemplified as thermosetting resins.

[0056] In particular, thermosetting resins are preferable because fusion bonding is not apt to occur even when heat is generated by local contact due to eccentricity of axis. Especially preferred thermosetting resins are epoxy resins, phenol resins, cyanate resins and unsaturated polyester resins.

[0057] In order to form a wearing ring of a prescribed shape, a suitable molding method for the shape and the properties of the matrix resin may be used. Molding methods will be described below concerning a cylindrical wearing ring, which is of a representative shape. For example, according to a molding method called sheet rolling molding, a sheet-like unidirectional prepreg or fabric prepreg is formed by impregnating carbon fibers with a matrix resin by a known method, a prescribed number of such prepregs are laminated on a mandrel, and after that, the laminated product is removed from the mandrel after setting by heating in the case of a thermosetting resin, with the result that a cylindrical molded product of carbon fiber reinforced plastic is obtained. After that, the cylindrical molded product is cut to a prescribed length and is ground and polished with a prescribed accuracy in order to make an accurate clearance, whereby a cylindrical wearing ring is obtained.

[0058] Also, by the filament winding lamination method, which is known as another lamination method, a tow-prepreg obtained by impregnating carbon fibers with a matrix resin can be laminated in a necessary number of layers by winding the tow-prepreg while orienting it. Also, a tow-prepreg may be woven to form a cylindrical shape. Alternatively, carbon fibers may be woven into a cylindrical shape and after that, the woven carbon fibers may be impregnated with a matrix resin

[0059] In an embodiment of the invention, the preferable cylindrical molded product is obtained, using sheet rolling molding, by alternately repeating the sequence of lamination of 1 to 10 layer(s) of unidirectional prepreg in the circumferential direction and the sequence of lamination of 1 to 10 layer(s) of unidirectional prepreg in the axial direction. On that occasion, the sheet-like prepreg is selected so that the thickness of each layer becomes about 0.05 to about 0.3 mm after setting, and the total number of layers is appropriately changed according to the thickness of one layer and the thickness of the wearing ring. In the case of a general thickness, the total number of layers is, for example, 20 to 300 or so. Furthermore, it is preferable that as the outermost layer of the wearing ring, which is the sliding surface thereof, (at least either on the outer side or inner side of the cylinder), a fabric prepreg be laminated in 1 to about 10 layers and particularly in 1 to about 5 layers. When the outermost layer is formed by a fabric prepreg, this provides the advantage that fluff is not apt to be formed during grinding and polishing.

[0060] A wearing ring formed of a carbon fiber reinforced plastic, which has been thus formed into a cylindrical shape, is attached to a substrate (main body of case or main body of impeller), which has been formed so as to allow the attaching of the wearing ring, and after that, the wearing ring is used.

[0061] In this invention, when this wearing ring made of a carbon fiber reinforced plastic is to be used in a pump, the wearing ring may be used both as the case wearing ring and the impeller wearing ring, but may be used either one of the both wearing rings, as already described. Because in ordinary uses, high-temperature fluids are often handled and the temperature rise by rotation is larger on the impeller side. Therefore, when this wearing ring is used either one of the case side and the impeller side, it is generally preferable that the wearing ring be used on the impeller side.

[0062] And when the wearing ring of the invention is used on one side only, metals, ceramics, plastics, carbon, etc. can be used as the material for the counterpart of a pair of wearing rings. In particular, from the standpoint of workability and price, metals are preferable and particularly, stainless steels such as SUS304 and SUS403 are preferable because they have high wear-resistance and rust-resistance.

[0063] Embodiments

[0064] Next, the invention will be described in further detail by referring to embodiments. The pump used in the evaluation is an overhang centrifugal pump having the rating of a water head of 55 m, a capacity of 14 m³/h, an output of 3.70 kW and a number of revolutions of 2900 rpm. The shape of the pump is almost the same as that shown in FIG. 1. Although in the pump shown in FIG. 1 the wearing ring pair on the suction side and the wearing ring pair on the back side have different diameters and lengths, in the pump used here both wearing ring pairs are of the same shape.

[0065] Furthermore, in the pump performance measurement in the embodiments, by using water at about 20° C. as a fluid, the relationship between discharge rate and pump efficiency (simple efficiency=water power/shaft power×100), the relationship between discharge rate and total pressure, and the relationship between discharge rate and shaft power were determined by the methods specified in JIS.

[0066] <Embodiment 1>

[0067] Prepreg A of about 0.25 mm thickness having a carbon fiber content of about 55% by volume was produced by impregnating the carbon fiber made by Nippon Graphite Fiber Corporation XN-60 with a moisture-resistance epoxy resin, and prepreg B with a lamination thickness (thickness after lamination) of about 0.25 mm having a carbon fiber content of about 50% by volume was produced by impregnating the carbon fiber cloth made by Toray Industries, Inc. CO6343 with a moisture-resistance epoxy resin. Prepreg B was wound on a mandrel in 5 lamination layers of 0° orientation, prepreg A was wound in such a manner that 0° oriented layer and 90° oriented layer are alternately wound to form a total of 20 layers, prepreg B was further wound in 5 lamination layers of 0° oriented layers, and after that, thermosetting was effected. As a result, a cylindrical molded product having 102 mm in outside diameter and 87 mm in inside diameter was obtained.

[0068] This cylinder made of a carbon fiber reinforced plastic was cut to a predetermined length, ground and polished, and then worked into a shape 101.0 mm in outside diameter, 88.5 mm in inside diameter and 22.5 mm in length. After that, fixing-screw holes were bored and a wearing ring made of a carbon fiber reinforced was obtained. This wearing ring was attached to both of the suction side and back side of the impeller. This impeller wearing ring had a coefficient of thermal expansion in the radial direction of about 5×10⁻⁶/° C.

[0069] On the other hand, a case wearing ring made of SUS403 having an inside diameter of 101.1 mm was used both on the suction side and the back side. That is, the clearance of the wearing rings is 0.1 mm in diameter. The performance of this pump, i.e., the relationship between discharge rate and pump efficiency, the relationship between discharge rate and total pressure, and the relationship between discharge rate and shaft power are shown in FIG. 3, FIG. 4 and FIG. 5, respectively. Seizure did not occur in spite of this narrow clearance.

[0070] <Embodiment 2>

[0071] Prepreg B used in Embodiment 1 was also used in this embodiment. Prepreg B (plain weave fabric) was wound on a mandrel in 30 lamination layers so that the direction of carbon fibers became 0° orientation and 90° orientation, thermosetting was then effected and a cylindrical molded product having 102 mm in outside diameter and 87 mm in inside diameter was obtained. This cylinder was worked in the same manner as in Embodiment 1 and a wearing ring of the same size as in Embodiment 1, i.e., 101.0 mm in outside diameter, 88.5 mm in inside diameter and 22.5 mm in length was obtained. This wearing ring was attached to both of the suction side and back side of the impeller. This impeller wearing ring had a coefficient of thermal expansion in the radial direction of about 10×10⁻⁶/° C.

[0072] On the other hand, the same case wearing ring as in Embodiment 1 was used. The performance of this pump is shown in FIGS. 3, 4 and 5. Seizure did not occur in spite of this narrow clearance

[0073] <Comparative Example 1>

[0074] Impeller wearing rings made of SUS403 with an outside diameter of 100.7 mm and a length of 22.5 mm were used. On the other hands, the same case wearing rings made of SUS403 having an inside diameter of 101.1 mm as in Embodiment 1 were used. That is, the clearance of the wearing rings is 0.4 mm in diameter. In both the case wearing rings and the impeller wearing rings, the coefficient of thermal expansion in the radial direction was about 19×10⁻⁶/° C. The performance of this pump is shown in FIGS. 3 to 5. Seizure did not occur.

[0075] <Comparative Example 2>

[0076] Impeller wearing rings made of SUS403 with an outside diameter of 101.0 mm and a length of 22.5 mm were used and case wearing rings made of SUS403 having an inside diameter of 101.1 mm were used. That is, the clearance of the wearing rings is 0.1 mm in diameter. However, seizure occurred during the operation of the pump and stable pump operation was impossible.

[0077] As described above, according to the invention, it is possible to provide a wearing ring which enables a clearance between a case wearing ring and an impeller wearing ring to be maintained within a small fixed range even when the temperature rises due to rotation and when a high-temperature fluid is used, and a pump which is provided with the wearing ring, is excellent in stability and has a good efficiency. 

1. An inner-cylinder wearing ring or an outer-cylinder wearing ring each of which is used in a pair of wearing rings of the combination of inner-cylinder side and outer-cylinder side; wherein, the inner-cylinder wearing ring or the outer-cylinder wearing ring is formed of a carbon fiber reinforced plastic and has a coefficient of thermal expansion in the radial direction of −1×10⁻⁶/° C. to 30×10⁻⁶/° C.
 2. An inner-cylinder wearing ring or an outer-cylinder wearing ring according to claim 1, in which its coefficient of thermal expansion in the radial direction is 3×10⁻⁶/° C. to 20×10⁻⁶/° C.
 3. An inner-cylinder wearing ring or an outer-cylinder wearing ring according to claim 1, in which the above-described carbon fiber reinforced plastic contains carbon fibers oriented in the axial direction and carbon fibers oriented in the circumferential direction of the wearing ring and in which the ratio of (weight of axial carbon fibers): (weight of circumferential carbon fibers) is (1:10) to (100:10).
 4. An inner-cylinder wearing ring or an outer-cylinder wearing ring according to claim 3, in which the ratio of (weight of axial carbon fibers): (weight of circumferential carbon fibers) is (15:85) to (85:15).
 5. An inner-cylinder wearing ring or an outer-cylinder wearing ring according to claim 1, in which the carbon fibers in the carbon fiber reinforced plastic which constitutes an outermost layer of the inner-cylinder wearing ring or the outer-cylinder wearing ring are a fabric.
 6. An inner-cylinder wearing ring or an outer-cylinder wearing ring according to claim 1, in which a matrix resin contained in the carbon fiber reinforced plastic is a thermosetting resin.
 7. An inner-cylinder wearing ring or an outer-cylinder wearing ring according to claim 1, which is used in a pair of wearing rings in which a metal wearing ring is used as an opposed wearing ring.
 8. An inner-cylinder wearing ring or an outer-cylinder wearing ring according to claim 1, in which the carbon fiber reinforced plastic is fabricated of continuous carbon filaments whose tensile modulus is in the range of 49 Gpa to 950 GPa.
 9. An inner-cylinder wearing ring or an outer-cylinder wearing ring according to claim 1, which is used in a pump provided with an impeller having an impeller wearing ring and a pump casing having a case wearing ring.
 10. An inner-cylinder wearing ring according to claim
 1. 11. An inner-cylinder wearing ring according to claim 1, which is used in a pair of wearing rings in which a metal wearing ring is used as an opposed wearing ring.
 12. A pump having the inner-cylinder wearing ring or the outer-cylinder wearing ring according to claim
 9. 13. A pump having the inner-cylinder wearing ring according to claim
 9. 